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University of Toronto physics professor Sajeev John has been awarded the 2021 Herzberg Gold Medal, Canada's most prestigious science prize.Sylvie Li/Shoot Studio

As a rule, theoretical physicists are used to putting up their best ideas and then watching them crash and burn as soon as a colleague spots a flaw in their reasoning.

But in 1987, when a 30-year-old Princeton University researcher named Sajeev John was working on a paper about the concept of “photonic band gaps,” it dawned on him that what he was describing was certain to work.

“That’s when it really struck me,” he said. “I became sure in my mind that it was possible to trap light.”

The intuition proved correct. Dr. John – who moved to the University of Toronto in 1989 – saw his idea flourish and grow into an entire field. At its heart is a class of materials called photonic crystals whose properties can be used to confine and manipulate light. Today, they are used in optical coatings and telecommunications and medical devices. In future they could lead to more efficient solar panels and to quantum computers that run on light.

On Wednesday, Dr. John was named this year’s winner of the Herzberg gold medal – one of Canada’s most prestigious science prizes, bestowed annually by the Natural Sciences and Engineering Research Council.

The award, which recognizes contributions made over a scientist’s entire career, is just the latest for Dr. John, who has previously won Germany’s Humboldt Prize, Saudi Arabia’s King Faisal science prize and a Guggenheim Fellowship from the United States. In 2017, he was named an officer of the Order of Canada.

Born in India, Dr. John came to Canada when he was 4 and grew up in London, Ont., the child of academic parents. As a teenager his technical abilities were readily apparent, scoring him admission to the Massachusetts Institute of Technology for his undergraduate degree and then Harvard University, where he earned his PhD in 1984.

But while physics was his playground, the more challenging dilemma for Dr. John was what he could do with it that might prove useful. His PhD work had included the notion of localizing sound waves within a solid. Now he began to wonder if something similar might be possible with light.

The idea was pioneered separately but in parallel with Eli Yablonovitch, another researcher with links to Canada who was working at Bell Laboratories in New Jersey and thinking about what would become known as photonic crystals around the same time as Dr. John. Their papers were published side by side in the same issue of Physical Review Letters in June, 1987.

“It was a fundamental achievement,” said Jeff Young, an experimental physicist at the University of British Columbia whose team works on photonic crystals. Dr. Young added that the two papers were the first to show that the way light propagates through matter is not just an inherent property of the material itself, but something that can be altered by the right arrangement of atoms.

As a measure of the influence of the work, Dr. John’s 1987 paper has been referenced 13,600 times since publication, making him one of the most highly cited researchers in the world. And he is one of only a handful of Canadian scientists identified as potential Nobel laureates based on impact.

That impact extends to the PhD students he had trained. Among them is Mona Berciu, another UBC faculty member who trained under Dr. John in the mid-1990s.

“He gave me a lot of freedom to explore and to have fun trying to solve various problems,” she said, adding that Dr. John has an uncanny way of pointing students in the right direction.

Dr. Berciu also said that an important part of Dr. John’s success has been his staying power – namely “his ability to write important, relevant papers year after year.”

Lately that relevance has extended into the domain of renewable energy. Dr. John said that the idea that currently has him most excited relates to the fact that standard solar cells, which use silicon to turn sunlight into electricity, have limited efficiency because they only work well for certain wavelengths of light. The silicon is made relatively thick to absorb more light but that adds weight and stiffness.

Dr. John and his colleagues have been working on ideas for sculpting the surface of a solar cell to make it behave as a photonic crystal that can trap a broader range of sunlight and raise the overall efficiency of the collector. At the same time, the material would be far lighter and more flexible.

“You could coat it onto surfaces – automobiles, walls, maybe even clothing,” Dr. John said. “What we were able to show theoretically is that with this light-trapping mechanism, you could actually absorb as much or more sunlight” as the material used in solar cells today.

He said he is also involved in several other research projects including one that has taken him back to his PhD work with sound waves as a route to engineering better soundproofing materials. But in whichever way his work takes him, Dr. John added, he has often found himself guided by the words of Philip Anderson, the late Nobel-winning physicist who first hired him to come to Princeton.

“He once told me that when the crowd is all racing in one direction, be willing to walk in the opposite direction,” Dr. John said. “Because the untrodden path is where the important new discoveries are most likely to be made.”

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